1. Field
The present invention relates to a method of fabricating a semiconductor device, and more particularly to a chemical-mechanical polishing used in forming a shallow trench isolation (STI) structure.
2. Related Art
Japanese patent application publication JP-A-2007-329342 discloses a conventional chemical mechanical polishing used in forming an STI structure. A nitride film is employed as a stopper film in the disclosed chemical mechanical polishing. A selectivity or a removal rate ratio of an insulating film for filling a trench in the STI structure to a nitride film (SiO2/SiN) is at some level when the nitride film is used as a stopper in polishing the insulating film. However, polishing places a large load on an isolation pattern of the stopper film. As a result, there is a problem that an amount of stopper film removed in the isolation pattern is larger than in the other patterns. Furthermore, a pattern line width of wiring has been reduced with progress in structural refinement in the semiconductor fabrication process. This necessitates a reduction in the film thickness of the stopper film, and there is a problem that the nitride film has a definite limitation in the use as a stopper film.